1. Field of the Invention
The present invention relates to a magnetoresistance effect element, and a magnetoresistance effect sensor and magnetic information detecting system using same, and more particularly, to a magnetoresistance effect element for reading magnetic information recorded on a magnetic recording medium, and a magnetoresistance effect sensor and magnetic information detecting system using same.
2. Description of the Related Art
In the prior art, magnetic reading converters called magnetic resistance (MR) sensors or MR heads are known. These read data from the surface of a magnetic recording medium at a large linear density. MR sensors and the like detect a magnetic field by detecting changes in resistance produced by reading elements in accordance with the surrounding magnetic field, and converting these changes to a magnetic field signal. In this, a magnetic signal detected by a reading element is detected as a function of the strength and direction of the magnetic flux. In a conventional MR sensor of this kind, one component of the resistance of the reading element changes in proportion to the square of the cosine (cos2) of the angle between the direction of magnetization and direction in which the sensor current flows through the element. This is called the xe2x80x98anisotropic magnetic resistancexe2x80x99 (AMR) effect.
This AMR effect is commonly known and therefore is not described here, but a detailed explanation thereof can be found, for example, in xe2x80x9cMemory, Storage and Related Applications,xe2x80x9d IEEE Trans. on Mag. MAG-11, p.1039 (1975), by D. A. Thompson, et. al. In magnetic heads using the AMR effect, often a longitudinal bias is applied in order to suppress Barkhausen noise, and in some cases, an anti-ferromagnetic material, such as FeMn, NiMn, nickel oxide, or the like, is used as a material for supplying this longitudinal bias.
Furthermore, recently, in resistance change in laminated magnetic sensors, remarkable magnetoresistance effects have been discovered due to spin-dependent transmissivity of conducting electrons between magnetic layers which are placed either side of a non-magnetic layer, and spin-dependent scattering at the accompanying layer interfaces. This magnetoresistance effect is known by various names, including xe2x80x9cmassive magnetoresistance effectxe2x80x9d or xe2x80x9cspin valve effectxe2x80x9d, or the like. Magnetic resistance sensors of this type are made from suitable materials, and they have improved sensitivity and display a greater resistance change with respect to magnetic field compared to sensors using the AMR effect. In MR sensors of this kind, the internal resistance in the plane between the ferromagnetic layers separated by a non-magnetic layer is proportional to the cosine of the angle between the directions of magnetization of the two layers.
Japanese Unexamined Patent 2-61572 which has a claim of priority based on an application dated Jun. 16th 1988 discloses a laminated magnetic structure which produces a high MR effect caused by non-parallel arrangement of the magnetization of the magnetic layers. In the aforementioned patent, ferromagnetic transition metals and alloys are cited as materials which can be used in this laminated magnetic structure. Furthermore, the patent also discloses that it is suitable to add an anti-ferromagnetic layer as one of the at least two magnetic layers separated by an intermediate layer, and FeMn is appropriate for this anti-ferromagnetic layer. A further MR sensor is disclosed in Japanese Unexamined Patent 4-358310 which has a claim of priority based on an application dated Dec. 11th 1990. This MR sensor comprises two thin film layers of ferromagnetic material divided by a thin film layer of non-magnetic metallic material. When the applied magnetic field is zero, the directions of magnetization of the two ferromagnetic thin film layers are orthogonal, and the resistance between the two unconnected ferromagnetic layers changes in direct proportion to the cosine of the angle between the directions of magnetization of the two layers, thereby producing an MR sensor which is not dependent on the direction of the electric current flowing through the MR sensor. Japanese Unexamined Patent 6-203340 which has a claim of priority based on an application dated Nov. 17th 1992 discloses an MR sensor which incorporates two thin film layers of ferromagnetic material separated by a thin film layer of non-magnetic metallic material. This MR sensor is based on the effect that when the applied external magnetic field is zero, the magnetization of the adjacent anti-ferromagnetic layer remains orthogonal with respect to the other ferromagnetic layer.
Furthermore, Japanese Unexamined Patent 7-262529 (application dated Mar. 24th 1994) discloses a magnetoresistance effect element which is a spin valve comprising a first magnetic layer/non-magnetic layer/second magnetic layer/anti-ferromagnetic, and more particularly one which uses CoZrNb, is CoZrMo, FeSiAl, FeSi, or NiFe, or a material wherein Cr, Mn, Pt, Ni, Cu, Ag, Al, Ti, Fe, Co, or Zn is added to these, in the first and second magnetic layers.
Furthermore, Japanese Unexamined Patent 7-202292 (application dated Dec. 27th 1993) discloses a magnetoresistance effect film characterized in that, in a magnetoresistance effect film comprising a plurality of magnetic thin films laminated between non-magnetic layers on a substrate, wherein an anti-ferromagnetic thin film is provided in one of the soft magnetic thin layers which are mutually adjacent via the non-magnetic thin layer, and Hc2 less than Hr, taking the bias magnetic field of this anti-ferromagnetic thin film as Hr and the coercive force of the other ferromagnetic thin film as Hc2, the aforementioned anti-ferromagnetic material is at least one of NiO, CoO, FeO, Fe2O3, MnO, or Cr, or a mixture of these.
Furthermore, Japanese Patent Application 6-21487 (application dated Sep. 8th 1994) and Japanese Patent Application 6-269524 (application dated Nov. 2nd 1994) propose a magnetoresistance effect film characterized in that, in the aforementioned magnetoresistance effect film, the anti-ferromagnetic material is a superlattice comprising at least two of NiO, NiXCol-XO and CoO. Japanese Patent Application 7-11354 (application dated Jan. 27th 1995) proposes a magnetoresistance effect film characterized in that, in the aforementioned magnetoresistance effect film, the anti-ferromagnetic material is a superlattice comprising at least two of NiO, NiXCol-XO (x=0.1xe2x88x920.9) and CoO, and the atomic ratio of Ni with respect to Co in this superlattice is equal to or greater than 1.0. Japanese Patent Application 7-136670 (application dated Jun. 2nd 1995) proposes a magnetoresistance effect film characterized in that, in the aforementioned magnetoresistance effect film, the anti-ferromagnetic material has a two-layer structure comprising CoO laminated to a thickness of 10-40 Angstrom on NiO. However, the magnetoresistance effect films using oxides in the anti-ferromagnetic layer, as disclosed in the aforementioned patent publications and applications, are subject to great stress in the oxide anti-ferromagnetic layer, and therefore a problem arises in that the anti-ferromagnetic layer peels away from the base layer due to local current heating effects when the sensor current passes through the element, thereby causing the element to break down.
The present invention was devised in order to resolve the aforementioned problems, and specifically, an object thereof is to provide an magnetoresistance effect element having excellent current tolerance characteristics such that the element does not break down due to peeling when the sensor current is passed, by adopting a composition wherein sufficient adhesive force is provided between the base layer and the anti-ferromagnetic layer.
It is a further object of the present invention to provide a magnetoresistance effect sensor and magnetic information detecting system having satisfactory properties, which use this magnetoresistance effect element having excellent current tolerance characteristics.
In order to achieve the aforementioned objects, in a magnetoresistance effect element wherein an anti-ferromagnetic layer, a fixed magnetic layer, a non-magnetic layer and a free magnetic layer are laminated successively onto a base layer, the magnetoresistance effect element according to the present invention comprises an adhesive layer for preventing peeling when current is passed, placed between the base layer and the anti-ferromagnetic layer formed by a single layer or multiple layers having Ni oxide, Co oxide or Fe oxide as a principal component, or a combination of these.
Furthermore, in a magnetoresistance effect element wherein an anti-ferromagnetic layer, a fixed magnetic layer, a non-magnetic layer and a free magnetic layer are laminated successively onto a base layer, and an enhancing layer is formed between the fixed magnetic layer and the non-magnetic layer and/or between the non-magnetic layer and the free magnetic layer, the magnetoresistance effect element according to the present invention comprises an adhesive layer for preventing peeling when current is passed, placed between the base layer and the anti-ferromagnetic layer formed by a single layer or multiple layers having Ni oxide, Co oxide or Fe oxide as a principal component, or a combination of Ni oxide, Co oxide or Fe oxide.
FIG. 7 shows adhesive force in a cases where alumina or SiO2 is used for the aforementioned base layer, and Ni oxide, Co oxide or Fe oxide are used in the anti-ferromagnetic layer. In contrast to this, the present invention is provided with an adhesive layer between the base layer and the oxide anti-ferromagnetic layer. FIG. 8 shows adhesive force (Gpa) at both interfaces in cases where alumina or SiO2 is used for the base layer, similarly to the foregoing, and a thin film of the different materials listed in the diagram is formed thereonto as an adhesive layer.
Moreover, FIG. 9 shows adhesive force (Gpa) at both interfaces in cases where a thin film of one of the materials listed in the diagram is used as an adhesive layer and Ni oxide, Co oxide or Fe oxide are formed thereonto as the anti-ferromagnetic layer.
The adhesive force between the various thin film materials given in FIG. 8 and the alumina or SiO2 film, and the adhesive force between the various thin film materials given in FIG. 9 and the Ni oxide, Co oxide or Fe oxide is greater in all cases than the bonding force between the alumina or SiO2 and Ni oxide, Co oxide or Fe oxide, as shown in FIG. 7. This means that the adhesive force between the alumina or SiO2 and Ni oxide, Co oxide or Fe oxide is increased by inserting one of the thin film materials given in FIG. 8 and FIG. 9 as an adhesive layer between the base layer of alumina or SiO2 and the anti-ferromagnetic layer of Ni oxide, Co oxide or Fe oxide.
Furthermore, the present invention uses a magnetoresistance effect element having an adhesive layer as the aforementioned magnetoresistance effect element in a shielded magnetoresistance effect sensor having a structure wherein a lower shield layer, a lower gap layer and a patterned magnetoresistance effect element are laminated successively onto a substrate, a longitudinal bias layer and lower electrode layer are laminated successively thereonto such that they contact the terminal section of the magnetoresistance effect element or overlap partially therewith, and an upper gap layer and upper shield layer are laminated successively onto the magnetoresistance effect element, longitudinal bias layer and the lower electrode layer.
Moreover, the present invention uses a magnetoresistance effect element having an adhesive layer as the aforementioned magnetoresistance effect element in a magnetic information detecting system comprising a magnetoresistance effect element, means for generating a current to pass through the magnetoresistance effect element, and means for detecting changes in the resistivity of the magnetoresistance effect element as a function of a detected magnetic field. The magnetic recording device according to the present invention may also be constituted using this magnetic information detecting system.